It is known that certain chlorine-based compounds, such as chlorine derivates of paraffinic hydrocarbon compounds referred to as chlorinated paraffins, can serve as lubricant additives to improve the performance of the lubricant under extreme pressure. Under normal lubricating conditions, the two metal surfaces will be separated by a thin film of lubricant which provides the required reduction in friction. Under situations of extreme pressure between the two metal surfaces, all the liquid lubricant is forced from the area of contact between the surfaces. Where an extreme pressure additive such as chlorinated paraffin is present, however, it has been found that the resultant heat generated between the two surfaces causes chlorine atoms to be liberated from the additive and to combine with the surface metal, such as iron, to form a chloride, such as iron chloride. This surface coating of chloride has a much lower coefficient of friction than the dry metal surface. The iron chloride surface coating tends to fill in depressions in the surfaces, resulting in smoother surfaces at the point of interaction and reduced friction and wear.
Chlorinated paraffins have been used as extreme pressure additives in such applications as metal-working. However, the corrosive nature of chlorinated paraffins have made them generally unsuitable for use in internal combustion engine applications or other corrosion-sensitive applications. Under heating, the chlorinated paraffins release hydrochloric acid, which is corrosive.
The lubrication regime described herein falls into the category of a boundary lubrication in which there is intimate or severe contact between two dissimilar metal surfaces or objects under high pressure, and in which the EP lubricant additives react to form metallic oxides generating sacrificial layers which are responsible for the lubricating performance. Therefore, the end-use applications which are particularly suited to this invention include, but are not limited to, internal combustion engines, transmission systems, gear boxes, bearings, etc. Lubricating oils typically also contain one or more of the following additives: boundary additives, corrosion inhibitors, anti-oxidants, dispersants, anti-wear additives, and extreme-pressure (“EP”) additives. Boundary, antiwear, and extreme-pressure additives are typically grouped as performance additives while the others as functional additives. This invention pertains to the use of nitrated extreme-pressure additives particularly in internal combustion engines, gear oils, as well as applications involving rubbing metal moving parts.
Presently, commercial extreme-pressure additives contain one or more sulfur, chlorine, or phosphorus-containing compounds. Sulfur-containing additives are sulfurized fat or fatty esters or synthetic polysulfides; chlorine-containing additives are chlorinated paraffins, olefins, or chlorinated fatty compounds; while phosphorus-containing additives consist of phosphate esters and phosphites. Each of the above-mentioned commercial extreme-pressure additives has its own set of limitations.
Sulfurized additives are effective for working with steel parts but not those involving stainless steel or special alloys such as titanium, chromium, or nickel-based, especially those in the most severe working environments. Phosphate esters or phosphites are excellent anti-wear or load-carrying additives but only in light-duty applications. For most cases, they are not effective extreme-pressure additives and definitely unsuitable for applications involving stainless steel. One of the reasons is that these phosphorus and sulfur-containing additives are not very reactive to hardened steel or low-iron metallic composites such as stainless or special alloys mentioned above. Chlorinated compounds, on the other hand, are very effective in wide range of metal processing applications involving both steel, stainless steel, and special alloys. The rule of thumb in the industry is that chlorinated additives are required for working with these exotic alloys of low or no iron content. However, recent environmental concern regarding the disposal of chlorinated compounds has prompted the lubricant industry to search for alternatives to replace the chlorinated additive workhorse.
This invention describes a novel class of extreme-pressure additives, labeled generically as “nitrated” or nitro compounds. The nitro compounds cited in this invention can be made by using 70% nitric acid or nitrogen dioxide gas to nitrate many classes of compounds, such as: (1) fatty acids with unsaturation; (2) fatty oils which contain unsaturation sites on their hydrocarbon chains such as vegetable oils, tall oil and animal fats; (3) esters (synthetic or natural) derived from the reaction of alcohols with fatty acids, such as triglycerides; (4) C2-C28 simple terminal or internal olefins, more preferably C8-C18 olefins; (5) C2-C20 polyolefins or C4-C20 polydiolefins, more preferably C2-C6 polyolefins containing terminal or internal unsaturation, preferably polyisobutylene (hereinafter “PIB”); (6) C8-C20 copolymers derived from polyolefins and vinyl aromatics e.g., poly(styrene butadiene); and (7) C4-C30 alkylated phenols, e.g., nonyl phenol and wherein the alkyl group is a straight or branched chain.
At least one novel feature of this additive is that it contains nitro-compounds instead of conventional elements such as sulfur, chlorine, or phosphorus, and has demonstrated its effectiveness as an extreme-pressure additive capable of replacing (either completely or at least partially) both sulfurized, chlorinated, and phosphated additives for use in internal combustion engines, both steel and stainless steel applications, for aluminum applications, as well as for processing metallic alloys which are currently considered as most challenging such as titanium, nickel, and chromium-based metals or alloys.
In one embodiment of the invention, these additives can be used synergistically with at least one non-chlorine containing additive. At least one feature of the nitrated additive is that it contains no or reduced amounts of conventional elements such as sulfur, chlorine, or phosphorus, and has demonstrated its effectiveness as an extreme-pressure additive capable of replacing or partially replacing sulfurized, phosphated, and primarily chlorinated EP additives for both steel and stainless steel, as well as the above-mentioned non-ferrous applications. In one preferred embodiment of the invention, this additive is used either by itself, or in synergistic combinations, in internal combustion engines, gear oils, and metallic applications wherein metal-to-metal contact is inherent, and in which the active elements in the lubricating oil chemically react with the metal surfaces.